The present invention relates to improved golf ball cover compositions produced by blending new metal cation neutralized high acid ionomer resins with ionomer resins containing a comonomer of the acrylate ester class. The improved golf ball cover compositions are useful for producing golf balls, particularly multi-piece balls, exhibiting enhanced overall travel distance and/or playability properties while maintaining or improving durability characteristics necessary for repetitive play.
Ionomeric resins are polymers containing interchain ionic bonding. As a result of their toughness, durability, and flight characteristics, various ionomeric resins sold by E. I. DuPont de Nemours and Company under the trademark xe2x80x9cSurlyn(copyright)xe2x80x9d and more recently, by the Exxon Corporation (see U.S. Pat. No. 4,911,451) under the trademarks xe2x80x9cEscor(copyright)xe2x80x9d and the tradename xe2x80x9cIotekxe2x80x9d, have become the materials of choice for the construction of golf ball covers over the traditional xe2x80x9cbalataxe2x80x9d (trans polyisoprene, natural or synthetic) rubbers. The softer balata covers, although exhibiting enhanced playability properties, lack the durability properties required for repetitive play.
Ionomeric resins are generally ionic copolymers of an olefin having from about 2 to about 8 carbon atoms, such as ethylene, and a metal salt of an alpha, beta-ethylenically unsaturated mono- or dicarboxylic acid such as acrylic acid, methacrylic acid or maleic acid. The pendent ionic groups in the ionomeric resins interact to form ion-rich aggregates contained in a non-polar polymer matrix. The metal ions, such as sodium, zinc, lithium, etc. are used to neutralize some portion of the acid groups in the copolymer resulting in a thermoplastic elastomer exhibiting enhanced properties, i.e. improved durability, etc. for golf ball construction over balata.
Generally, the ionic copolymers comprise one or more alpha-olefins and from about 9 to about 15 weight percent of alpha, beta-ethylenically unsaturated mono- or dicarboxylic acid, the basic copolymer neutralized with metal ions to the extent desired. Usually, at least 20% of the carboxylic acid groups of the copolymer are neutralized by the metal ions (such as sodium, zinc, lithium, and the like) and exist in the ionic state. In some instances, an additional softening comonomer can also be included to form a terpolymer.
Suitable olefins for use in preparing the ionomeric resins include ethylene, propylene, butene-1, hexene-1, and the like. Unsaturated carboxylic acids include acrylic, methacrylic, ethacrylic, xcex1-chloroacrylic, crotonic, maleic, fumaric, itaconic acids, and the like. The ionomeric resins utilized in the golf ball industry are generally copolymers of ethylene with acrylic (i.e. Escor(copyright)) and/or methacrylic (i.e. Surlyn(copyright)) acid. In addition, two or more types of ionomeric resins may be blended into the cover compositions in order to produce the desired properties of the resulting golf balls.
Along this line, the properties of the cover compositions and/or the ionomeric resins utilized in the golf ball industry vary according to the type and amount of the metal cation, the molecular weight, the composition of the base resin (i.e. the nature and the relative content of the olefin, the unsaturated carboxylic acid groups, etc.), the amount of acid, the degree of neutralization and whether additional ingredients such as reinforcement agents or additives are utilized. Consequently, the properties of the ionomer resins can be controlled and varied in order to produce golf balls having different playing characteristics, such as differences in hardness, playability (i.e. spin, feel, click, etc.), durability (i.e. impact and/or cut resistance), and resilience (i.e. coefficient of restitution).
However, while there are currently more than fifty commercial grades of ionomers available from DuPont and Exxon with a wide range of properties which vary according to the type and amount of metal cations, molecular weight, composition of the base resin (i.e. relative content of ethylene and methacrylic and/or acrylic acid groups), the degree of neutralization and additive ingredients such as reinforcement agents, etc., a great deal of research continues in order to develop golf ball cover compositions exhibiting not only the playability characteristics previously associated with the balata cover, but also the improved impact resistance and carrying distance properties produced by the ionomeric resins.
An object of the present invention is to provide golf ball cover compositions which, when utilized in golf ball construction, produce balls exhibiting improved overall travel distance and/or playability characteristics while maintaining satisfactory durability properties.
Along this line, two of the principal properties involved in the performance of golf balls are resilience and hardness. Resilience (i.e. coefficient of restitution), along with ball size, weight and additional factors such as club head speed, angle of trajectory, and ball aerodynamics (i.e., dimple pattern), generally determine the distance a ball will travel when hit. Since club head speed and the angle of trajectory are not factors easily controllable, particularly by golf ball manufacturers, the factors of concern among manufacturers are the coefficient of restitution and the surface dimple pattern of the ball.
A golf ball""s coefficient of restitution (C.O.R.) is the ratio of the relative velocity of the ball after direct impact to that before impact. One way to measure the coefficient of restitution is to propel a ball at a given speed against a hard massive surface, and measure its incoming velocity and outgoing velocity. The coefficient of restitution is defined as the ratio of the outgoing velocity to incoming velocity of a rebounding ball and is expressed as a decimal. As a result, the coefficient of restitution can vary from zero to one, with one being equivalent to an elastic collision and zero being equivalent to an inelastic collision.
The coefficient of restitution of a one-piece golf ball is a function of the ball""s composition. In a two-piece or a multi-layered golf ball, the coefficient of restitution is a function of the core, the cover and any additional layer. While there are no United States Golf Association (U.S.G.A.) limitations on the coefficient of restitution values of a golf ball, the U.S.G.A. requires that the golf ball cannot exceed an initial velocity of 255 feet/second. As a result, golf ball manufacturers generally seek to maximize the coefficient of restitution of a ball without violating the velocity limitation.
The hardness of the ball is the second principal property involved in the performance of a golf ball. The hardness of the ball can affect the playability of the ball on striking and the sound or xe2x80x9cclickxe2x80x9d produced. Hardness is determined as the deformation (i.e. compression) of the ball under various load conditions applied across the ball""s diameter (i.e. the lower the compression value, the harder the material). As indicated in U.S. Pat. No. 4,674,751, xe2x80x9csofterxe2x80x9d covers permit the accomplished golfer to impart proper spin. This is because the softer covers deform on impact significantly more than balls having xe2x80x9charderxe2x80x9d ionomeric resin covers. As a result, this allows the better player to impart fade, draw, or backspin to the ball thereby enhancing playability. Such properties can be determined by various xe2x80x9cspin rate testsxe2x80x9d, such as the xe2x80x9cnine-ironxe2x80x9d spin rate test set forth below.
In various attempts to produce a high coefficient of restitution golf ball exhibiting the enhanced travel distance desired, the golfing industry has blended various ionomeric resins. However, many of these blends do not exhibit the durability and playability characteristics necessary for repetitive play and/or the enhanced travel distance desired.
The present invention is directed, in part, to the preparation of new cation neutralized ionomer resins containing relative high amounts of acid (i.e. greater than 16 weight percent acid, preferably from about 17 to about 25 weight percent acid, and more preferably from about 18.5 to about 21.5 weight percent acid) and partially neutralized with sodium, manganese, lithium, potassium, zinc, magnesium, calcium and nickel ions. The new cation neutralized high acid ionomers produce, when blended and melt processed according to the parameters set forth below, cover compositions exhibiting enhanced coefficient of restitution values when compared to low acid ionomers, or blends of low acid ionomer resins containing 16 weight percent acid or less. The new high acid ionomer cover compositions produce golf balls which exhibit properties of enhanced carrying distance (i.e. possess higher coefficient of restitution values) over known ionomer blends such as those set forth in U.S. Pat. Nos. 4,884,814, 4,911,451 and 5,120,791.
Along this line, until relatively recently, all of the ionomer resins commercially available contained at most 15 to 16 weight percent carboxylic acid. These are now defined by the present inventor as being xe2x80x9clow acidxe2x80x9d ionomer resins. In 1989, the Research and Development Division of DuPont formulated one or more ionomer resins containing greater than 15 weight percent acid and indicated that these new ionomers may have some use in previously known ionomer resin applications. Specifically, DuPont suggested in a brief Research Disclosure (E. I. DuPont de Nemours and Co., Research Disclosure No. 297,003) that ionomers produced from polymers of ethylene acrylic acid or methacrylic acid containing greater than 15 weight percent acid can be melt processed to produce articles (i.e. golf balls, foot wear, ski boots, cosmetic bottle cap closures and so on) with good properties (i.e. improved stiffness, hardness and clarity) when compared with ionomers with lower acid levels.
However, not only has little information been provided concerning the acid levels and types of effective ionomers, particularly with respect to the art of golf ball manufacturing, it has been found that many cover compositions produced from polymers of ethylene/acrylic acid or ethylene/methacrylic acid containing greater than 15 weight percent acid were unsatisfactory in that these compositions exhibit processing problems or were generally short on distance and/or durability and thus, were not particularly commercially viable. Similar poor results were produced with covers composed of blends of high and low acid ethylene/acrylic acid or ethylene/methacrylic acid polymers and/or covers produced from single high acid ionomers containing greater than 15 weight percent acid.
However, notwithstanding the above difficulties, it has been discovered that improved golf ball covers can be produced from specific blends of high acid ionomers (i.e. ionomer resins containing greater than 16 weight percent acid, preferably from about 17 to about 25 weight percent acid, and more preferably from about 18.5 to about 21.5 weight percent acid) which do not exhibit the processing, distance and/or durability limitations demonstrated by the prior art.
In this regard, it has been found that blends of specific high acid ionomer resins, particularly blends of sodium and zinc high acid ionomers, as well as blends of sodium and magnesium high acid ionomers, extend, when utilized in golf ball cover construction, the range of hardness beyond that previously obtainable while maintaining the beneficial properties (i.e. durability, click, feel, etc.) of the softer low acid ionomers disclosed in U.S. Pat. Nos. 4,884,814 and 4,911,451. These blends produce harder, stiffer golf balls having higher C.O.R. values, and thus longer distance. This discovery is the subject matter of U.S. application Ser. No. 776,803, filed on Oct. 15, 1991, and currently co-pending herewith.
In addition, a number of new high acid ionomers, particularly new metal cation neutralized acrylic acid based high acid ionomer resins have been developed by the present inventor, which exhibit, when utilized for golf ball cover construction, cover compositions having further improved hardness and resilience (C.O.R.) properties. The new metal cation neutralized acrylic acid based high acid ionomer resins, as well as specific blends of these resins, are particularly valuable in the field of golf ball production.
Furthermore, as a result of the development of a number of new acrylic acid based high acid ionomers neutralized to various extents by several different types of metal cations, such as by manganese, lithium, potassium, calcium and nickel cations, several new high acid ionomers and/or high acid ionomer blends besides sodium, zinc and magnesium high acid ionomers or ionomer blends are now available for golf ball cover production. It has been found that many of these new cation neutralized high acid ionomer blends produce cover compositions exhibiting enhanced resilience (i.e. longer distance) due to synergies which occur during processing. Consequently, the new metal cation neutralized acrylic acid based high acid ionomer resins may be blended to produce substantially harder golf balls having higher C.O.R. values than those produced by the low acid ionomer covers presently commercially available.
Moreover, it has been further discovered that the new cation neutralized high acid ionomers produce, when blended with low acid ionomer resins containing an unsaturated comonomer of the acrylate ester class having from 1 to 21 carbon atoms, and melt processed according to the parameters set forth below, cover compositions exhibiting enhanced playability and durability characteristics. Consequently, the addition of the ionomer resin containing the acrylate comonomer to the new cation neutralized high acid ionomers are useful in preparing softer ionomer blends that have utility in softer cover golf balls such as the Top-Flite(copyright) Tour and Tour Edition(copyright) golf balls produced by Spalding and Evenflo Companies, Inc., the assignee of the present invention.
These and other objects and features of the invention will be apparent from the following description and from the claims.
In one aspect, the present invention is directed to improved cover compositions for golf ball construction and to the resulting golf balls produced thereby. The novel golf ball cover compositions of the invention comprise blends of recently developed metal cation neutralized high acid ionomer resins and ionomer resins containing a comonomer of the acrylate ester class. When the cover compositions are used to manufacture golf balls, the golf balls produced thereby exhibit properties of improved overall distance (resilience), playability (i.e. softness and spin) and/or durability when compared to golf balls produced by blends of high acid ionomer resins and/or blends of low acid ionomer resins. The cover compositions of the present invention are also useful in preparing softer covers that have utility in soft covered balls such as Top-Flite(copyright) and Tour Edition(copyright) balls trademarked and sold by Spalding and Evenflo Companies, Inc., without the necessity of using only those ionomer resins commercially available from DuPont or Exxon.
In another aspect, the instant invention relates to a golf ball comprising a core and a cover. The cover is comprised of a blend of a copolymer consisting of a recently developed metal cation neutralized high acid ionomer and a ionomer resin containing a softening comonomer of the acrylate ester class. The metal cation neutralized high acid ionomer resin is a copolymer of greater than 16% by weight of an alpha, beta-unsaturated carboxylic acid (preferably from about 17% to about 25% by weight acid, and more preferably from about 18.5% to about 21.5% by weight acid) and an alpha-olefin, of which 10% to 90% of the carboxyl groups of the copolymer are neutralized with a metal cation. The ionomer resin containing a softening comonomer of the acrylate ester class is a metal salt of an acid terpolymer of an olefin having from about 2 to 8 carbon atoms, an alpha, beta-unsaturated carboxylic acid, and an unsaturated monomer of the acrylate ester class having from 1 to 21 carbon atoms. In addition, the cover may contain one or more additional ingredients such as pigments, dyes, U.V. absorbers and optical brighteners.
In still a further aspect, the invention is directed to a golf ball comprising a core and a cover, wherein the cover is comprised of a metal cation neutralized high acid ionomer resin which is a copolymer of greater than 16% by weight of an alpha, beta-unsaturated carboxylic acid, (preferably from about 17% to about 25% by weight acid, and more preferably from about 18.5% to about 21.5% by weight acid) and an olefin, of which 10% to 90% of the carboxyl groups of the copolymer are neutralized with one or more metal cations selected from the group consisting of sodium, zinc, magnesium, manganese, lithium, potassium, calcium and nickel; and, ii) an ionomer resin containing a softening acrylate comonomer which is a terpolymer of an olefin having from about 2 to 8 carbon atoms, an alpha, beta-unsaturated carboxylic acid and an unsaturated monomer of the acrylate ester class having from 1 to 21 carbon atoms of which 10% to 90% of the carboxyl groups of the terpolymer are neutralized with one or more metal cations selected from the group consisting of sodium, zinc, magnesium, manganese, lithium, potassium, calcium and nickel. Moreover, the cover may contain of one or more additional ingredients such as pigments, dyes, U.V. absorbers and optical brighteners.
In a further additional aspect, the invention concerns the preparation of a golf ball cover composition having the improved combination of playability, durability and/or travel distance properties by the first pre-blending of a high acid copolymer with an acid terpolymer containing a softening comonomer of the acrylate ester class followed by neutralization of the blended mixture with one or more metal cations. By the in-situ pre-blending of a high acid copolymer with an acid terpolymer containing a softening acrylate termonomer, followed by neutralization of the copolymer/terpolymer mixture with one or more metal cations, improvements in the overall combination of characteristics such as C.O.R., spin and scuff/abrasion resistance can be produced.
Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art.
The present invention relates to the development of a number of new metal cation neutralized high acid ionomers, and to the use of these new metal cation neutralized high acid ionomers in combination with ionomer resins containing additional softening comonomers of the acrylate ester class for the purpose of producing golf ball covers exhibiting enhanced overall distance, playability and/or durability characteristics.
In this regard, several new metal cation neutralized high acid ionomer resins have been produced by the present inventor by neutralizing, to various extents, high acid copolymers of an alpha-olefin and an alpha, beta-unsaturated carboxylic acid with a wide variety of different metal cation salts. More particularly, it has been found that numerous new metal cation neutralized high acid ionomer resins can be obtained by reacting a high acid copolymer (i.e. a copolymer containing greater than 16% by weight acid, preferably from about 17 to about 25 weight percent acid, and more preferably about 20 weight percent acid), with a metal cation salt capable of ionizing or neutralizing the copolymer to the extent desired (i.e. from about 10% to 90%).
The base copolymer is made up of greater than 16% by weight of an alpha, beta-unsaturated carboxylic acid and an alpha-olefin. Generally, the alpha-olefin has from 2 to 10 carbon atoms and is preferably ethylene, and the unsaturated carboxylic acid is a carboxylic acid having from about 3 to 8 carbons. Examples of such acids include acrylic acid, methacrylic acid, ethacrylic acid, chloroacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid, with acrylic acid being preferred.
Consequently, examples of a number of copolymers suitable for use in the invention include, but are not limited to, high acid embodiments of an ethylene/acrylic acid copolymer, an ethylene/methacrylic acid copolymer, an ethylene/itaconic acid copolymer, an ethylene/maleic acid copolymer, etc. The base copolymer broadly contains greater than 16% by weight unsaturated carboxylic acid, and less than 84% by weight alpha-olefin. Preferably, the copolymer contains about 20% by weight unsaturated carboxylic acid and about 80% by weight ethylene. Most preferably, the copolymer contains about 20% acrylic acid with the remainder being ethylene.
Along these lines, examples of the preferred high acid base copolymers which fulfill the criteria set forth above, are a series of ethylene-acrylic copolymers which are commercially available from The Dow Chemical Company, Midland, Mich., under the xe2x80x9cPrimacorxe2x80x9d designation. These high acid base copolymers exhibit the typical properties set forth below in Table 1.
Due to the high molecular weight of the Primacor 5981 grade of the ethylene-acrylic acid copolymer, this copolymer is the more preferred grade utilized in the invention.
The metal cation salts utilized in the invention are those salts which provide the metal cations capable of neutralizing, to various extents, the carboxylic acid groups of the high acid copolymer. These include acetate, oxide or hydroxide salts of lithium, calcium, zinc, sodium, potassium, nickel, magnesium, and manganese.
Examples of such lithium ion sources are lithium hydroxide monohydrate, lithium hydroxide, lithium oxide and lithium acetate. Sources for the calcium ion include calcium hydroxide, calcium acetate and calcium oxide. Suitable zinc ion sources are zinc acetate dihydrate and zinc acetate, a blend of zinc oxide and acetic acid. Examples of sodium ion sources are sodium hydroxide and sodium acetate. Sources for the potassium ion include potassium hydroxide and potassium acetate. Suitable nickel ion sources are nickel acetate, nickel oxide and nickel hydroxide. Sources of magnesium include magnesium oxide, magnesium hydroxide, magnesium acetate. Sources of manganese include manganese acetate and manganese oxide.
The new metal cation neutralized high acid ionomer resins of the invention are produced by reacting the high acid base copolymer with various amounts of the metal cation salts above the crystalline melting point of the copolymer, such as at a temperature from about 200xc2x0 F. to about 500xc2x0 F., preferably from about 250xc2x0 F. to about 350xc2x0 F. under high shear conditions at a pressure of from about 100 psi to 10,000 psi. Other well known blending techniques may also be used. The amount of metal cation salt utilized to produce the new metal cation neutralized high acid based ionomer resins is the quantity which provides a sufficient amount of the metal cations to neutralize the desired percentage of the carboxylic acid groups in the high acid copolymer. The extent of neutralization is generally from about 10% to about 90%.
As indicated more specifically in Example 1 below, a number of new types of metal cation neutralized high acid ionomers can be obtained from the process of this invention. These include new high acid ionomer resins neutralized to various extents with manganese, lithium, potassium, calcium and nickel cations. In addition, when a high acid ethylene/acrylic acid copolymer is utilized as the base copolymer component of the invention and this component is subsequently neutralized to various extents with the metal cation salts producing acrylic acid based high acid ionomer resins neutralized with cations such as sodium, potassium, lithium, zinc, magnesium, manganese, calcium and nickel, several new cation neutralized acrylic acid based high acid ionomer resins are produced.
When compared to low acid versions of similar cation neutralized ionomer resins, the new metal cation neutralized high acid ionomer resins exhibit enhanced hardness, modulus and resilience characteristics. These are properties that are particularly desirable in a number of thermoplastic fields, including the field golf ball manufacturing.
Moreover, as a result of the development of a number of new acrylic acid based high acid ionomer resins neutralized to various extents by several different types of metal cations, such as manganese, lithium, potassium, calcium and nickel cations, several new ionomers or ionomer blends are now available for golf ball production. By using the high acid ionomer resins of the present invention, harder, stiffer golf balls having higher C.O.R.s, and thus longer distance, can be obtained.
Examples of high acid methacrylic acid based ionomers include Surlyn(copyright) AD-8422 (sodium cation), Surlyn(copyright) 8162 (zinc cation), Surlyn(copyright) SEP-503-1 (an experimental zinc cation), and Surlyn(copyright) SEP-503-2 (an experimental magnesium cation). According to DuPont, all of these ionomers contain from about 18.5% to about 21.5% by weight methacrylic acid.
More particularly, Surlyn(copyright) AD-8422, is currently (as of January, 1992) commercially available from DuPont in a number of different grades (i.e. AD-8422-2, AD-8422-3, AD-8422-5, etc.) based upon differences in melt index. According to DuPont, Surlyn(copyright) AD-8422 offers the following general properties when compared to Surlyn(copyright) 8920 the stiffest, hardest of all of the low acid grades (referred to as xe2x80x9chardxe2x80x9d ionomers in U.S. Pat. No. 4,884,814):
In comparing Surlyn(copyright) 8920 to Surlyn(copyright) 8422-2 and Surlyn(copyright) 8422-3, it is noted that the high acid Surlyn(copyright) 8422-2 and 8422-3 ionomers have a higher tensile yield, lower elongation, slightly higher Shore D hardness and much higher flexural modulus. Surlyn(copyright) 8920 contains 15 weight percent methacrylic acid and is 59% neutralized with sodium.
In addition, Surlyn(copyright) SEP-503-1 (an experimental zinc cation neutralized high acid methacrylic acid based ionomer resin) and Surlyn(copyright) SEP-503-2 (an experimental magnesium cation neutralized high acid methacrylic acid based ionomer resin) are high acid zinc and magnesium versions of the Surlyn(copyright) AD 8422 high acid ionomers. When compared to the Surlyn(copyright) AD 8422 high acid ionomers, the Surlyn(copyright) SEP-503-1 and SEP-503-2 ionomers can be defined as follows:
Furthermore, Surlyn(copyright) 8162 is a zinc cation neutralized methacrylic acid based high acid ionomer resin containing approximately 20% by weight (i.e. 18.5-21.5% weight) methacrylic acid copolymer that has been 30-70% neutralized. Surlyn(copyright) 8162 is currently (as of January, 1992) commercially available from DuPont.
For comparison purposes, examples of commercially available low acid methacrylic acid based ionomer resins are set forth below. These are many of the xe2x80x9chardxe2x80x9d ionomers utilized in the cover composition disclosed in U.S. Pat. No. 4,884,814. Along this line, the low acid ionomer resin cover compositions disclosed in the ""814 patent are generally considered to be among the best prior art methacrylic acid based cover compositions currently available from Spalding and Evenflo Companies, Inc., the assignee of the present application and U.S. application Ser. No. 776,803.
Examples of existing high acid acrylic acid based ionomer resins include the Escor(copyright) or the Iotek acrylic acid based high acid ionomers recently experimentally produced by Exxon. In this regard, Escor(copyright), or Iotek, 959 is a sodium ion neutralized ethylene-acrylic acid copolymer and Escor(copyright), or Iotek, 960 is a zinc neutralized ethylene-acrylic acid copolymer. According to Exxon, Ioteks 959 and 960 contain from about 19.0 to about 21.0% by weight acrylic acid with approximately 30 to about 70 percent of the acid groups neutralized with sodium and zinc ions respectfully. The physical properties of these high acid acrylic acid based ionomers are as follows:
For comparison purposes, examples of commercially available low acid acrylic acid based ionomer resins, such as these utilized in U.S. Pat. No. 4,911,451 are set forth below.
According to the present invention, it has been found that when the above indicated new metal cation neutralized acrylic acid based high acid ionomers, are processed according to the parameters set forth below to produce the covers of multi-layered golf balls, the resulting golf balls will travel further than previously known low acid ionomer resin covers and/or covers produced from high acid ionomers and/or high acid/low acid ionomer blends due to the balls"" enhanced coefficient of restitution values. This is particularly important in that an improvement of 0.001 in C.O.R. generally relates to an improvement of about 0.2 to 0.5 yards in travel distance.
When blends of two of the above indicated metal cation neutralized acrylic acid high acid ionomers are used (i.e. xe2x80x9cdibendsxe2x80x9d), the ratio of one type of metal cation neutralized acrylic acid high acid ionomer to another is generally from about 75% to about 25% and from about 25% to about 75%. In addition, xe2x80x9ctriblendsxe2x80x9d can also be formulated utilizing the new metal cation neutralized acrylic acid based high acid ionomers of the present invention. The general ratio for such xe2x80x9ctriblendsxe2x80x9d is 33.33%/33.33%/33.33% by weight.
However, notwithstanding the above indicated improvements in hardness and travel distance properties produced by the new metal cation neutralized high acid ionomers, it has also been further found that improvements in playability (i.e. enhanced Riehle compression, higher spin rates, lower Shore hardness, etc.) and durability (i.e. scuff resistance, etc.) characteristics can be obtained by blending the new high acid ionomers with ionomer resins containing a softening comonomer of the acrylate ester class. The addition of the ionomer resins containing the softening comonomer of the acrylate ester class to the high acid ionomer resins produces a significant increase in playability characteristics (i.e. spin rates, etc.) with only moderate decreases in C.O.R. and hardness values depending upon the amount of terpolymer incorporated.
Moreover, it was also observed that the addition of the ionomer resins containing the softening comonomer of the acrylate ester class generates enhanced cut resistance values, particularly in comparison with Spalding""s current Tour Edition(copyright) balls. This is of some importance since the Spalding Tour Edition(copyright) balls are considered to be generally among the best prior art balls exhibiting enhanced playability properties while maintaining reasonable travel distance characteristics.
Consequently, the blends of the new metal cation neutralized high acid ionomer and the ionomer resins (i.e. metal cation neutralized terpolymers) containing a softening comonomer of the acrylate ester class are useful in preparing softer ionomer resins that have utility in producing soft covered golf balls such as Spalding, Top-Flite(copyright) Tour and Tour Edition(copyright) balls. While these balls could only previously be manufactured utilizing hard/soft blends of commercially available low acid ionomers (i.e. U.S. Pat. Nos. 4,884,414 and 5,120,791), the present invention allows for the production of golf ball covers exhibiting even further enhanced properties (i.e. superior cut resistance, durability, etc.) through the use of non-commercially available ionomer resins, i.e. through the use of the recently formulated high acid ionomer resins.
In addition, it has also been found that the new cover composition can be produced xe2x80x9cin-situxe2x80x9d by first pre-blending a high acid copolymer, such as a poly(ethylene-acrylic acid) or poly(ethylene-methacrylic acid), with an acid terpolymer containing a softening comonomer (or termonomer) of the acrylate ester class, such as poly(ethylene-acrylic acid-methyl acrylate), poly (ethylene-methacrylic acid-butyl acrylate) etc., followed by neutralization of the blended mixture with one or more metal cations. By the in-situ pre-blending of the acid copolymer and the acid terpolymer and then the subsequent neutralization of the copolymer/terpolymer blend with a wide variety of metal cations, or mixtures thereof, further improvements in C.O.R., spin and scuff/abrasion resistance can be produced.
The ionomer resin containing the softening comonomer of the acrylate ester class is a metal salt of an acid terpolymer comprising an alpha-olefin having from about 2 to about 8 carbon atoms, an alpha, beta-unsaturated carboxylic acid, and an unsaturated monomer of the acrylate ester class having from 1 to 21 carbon atoms. The alpha-olefin is preferably ethylene. Suitable acids include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid, with acrylic and methacrylic acid being the preferred acids. The softening comonomer is preferably an alkyl acrylate with methyl acrylate and butyl acrylate being the most preferred. Examples of acid terpolymers suitable for use in the invention include poly(ethylene-methacrylic acid-butyl acrylate), poly(ethylene-acrylic acid-methyl acrylate), etc.
The acid terpolymer contains from about 40 to about 85% by weight alpha-olefin, from about 2 to about 20% by weight of unsaturated carboxylic acid, and from about 10 to about 40% by weight of the softening acrylate comonomer. Preferably, the terpolymer contains from about 65 to about 85% by weight ethylene, from about 5 to about 20% by weight unsaturated carboxylic acid, and from about 10 to about 30% by weight of the softening acrylate comonomer. More preferably, the acid terpolymer contains from about 69 to about 84 by weight ethylene, from about 6 to about 10% by weight acrylic acid or methacrylic acid and from about 10 to about 21% by weight methyl acrylate or butyl acrylate.
Representations of acid terpolymers which fulfill the criteria set forth above include a series ethylene/methacrylic acid/butyl acrylate terpolymers (i.e. poly[ethylene-methacrylic acid-butyl acrylate]) produced and sold by DuPont under the trade designation xe2x80x9cNucrel(copyright) 035xe2x80x9d and xe2x80x9cNucrel(copyright) 010xe2x80x9d. The typical properties of these terpolymers are set forth below:
These terpolymers consist essentially of about 80% by weight ethylene, about 10% by weight acrylic acid and about 10% by weight iso-butyl acrylate.
Examples of suitable ethylene/acrylic acid/methyl acrylate terpolymers (i.e. poly(ethylene acrylic acid-methyl acrylate)) include those acid terpolymers produced and sold by Exxon under the designation xe2x80x9cEscor ATXxe2x80x9d.
The typical properties of these terpolymers are set forth below:
The xe2x80x9cEscor ATXxe2x80x9d acid terpolymers consist essentially of about 72% to about 77% by weight ethylene, about 2% to about 7% by weight acrylic acid and about 21% by weight methyl acrylate.
By reacting the acid terpolymer with a metal cation salt capable of ionizing or neutralizing the carboxylic acid groups of the acid terpolymer to the extent desired (i.e. from about 10% to about 100%), the ionomer resin containing the softening comonomer of the acrylate ester class is produced. The processes and metal cation salts utilized in the invention to neutralized the terpolymer are essentially the same as those utilized to neutralize the high acid copolymer set forth above. The metal cation neutralized terpolymer containing the acrylate softening comonomer have a hardness from about 20 to about 45 as measured on the Shore D scale and a flexural modulus from about 1,500 to about 15,000 psi as measured in accordance with ASTM method D-790.
When the metal cation neutralized terpolymers containing the acrylate softening comonomer are blended with the new metal cation neutralized high acid ionomers described above, in the combinations more clearly define below and demonstrated in the Examples, and the blends are used to produce a golf ball cover, a more desirable golf ball in the terms of overall distance, playability and/or durability characteristics can be obtained. Moreover, in addition to the dry blending of the different ionomer resins, the new cover compositions can also be produced xe2x80x9cin-situxe2x80x9d by first pre-blending the high acid copolymer with the acid terpolymer containing the softening acrylate ester comonomer prior to neutralization with one or more metal cations.
The enhanced golf balls of the present invention containing the improved new metal cation neutralized terpolymers containing a comonomer of the acrylate ester class can be generally produced from a central core and an outer cover wherein the outer cover is made from a composition comprised of a blend of about 90 to about 10% of a metal cation neutralized high acid onomer, and of about 10 to about 90% of a metal cation neutralized terpolymer containing a comonomer of the acrylate ester class. In a preferred aspect, the ratio of high acid ionomer to the relatively soft ionomer is either (i) 60 to 40% or (ii) 50 to 50% high acid ionomer to the softer comonomer.
More preferably, it has been found that golf balls exhibiting properties of enhanced overall distance (i.e. higher C.O.R. values), playability (i.e. higher spin rates, etc.) and/or durability characteristics, can be produced from a core and a cover, wherein the cover is made from a composition comprised of about 80 to about 20% of a high acid ionomer resin and from about 20 to 80% of an ionomer resin containing a comonomer of the acrylate ester class, depending upon the C.O.R. value and/or the degree of softness desired. The optimal ranges of the high acid ionomer resin to the ionomer resins containing the softening comonomer of the acrylate ester class are from about 60 to about 40% high acid ionomer resin and from about 40 to about 60% of the ionomer resins containing the softening comonomer of the acrylate ester class.
Additional compatible additive materials may also be added to the compositions of the present invention, such as dyes (for example, Ultramarine Blue sold by Whitaker, Clark, and Daniels of South Painsfield, N.J.), and pigments, i.e. white pigments such as titanium dioxide (for example Unitane 0-110) zinc oxide, and zinc sulfate, as well as fluorescent pigments. As indicated in U.S. Pat. No. 4,884,814, the amount of pigment and/or dye used in conjunction with the polymeric cover composition depends on the particular base ionomer mixture utilized and the particular pigment and/or dye utilized. The concentration of the pigment in the polymeric cover composition can be from about 1% to about 10% as based on the weight of the base ionomer mixture. A more preferred range is from about 1% to about 5% as based on the weight of the base ionomer mixture. The most preferred range is from about 1% to about 3% as based on the weight of the base ionomer mixture. The most preferred pigment for use in accordance with this invention is titanium dioxide.
Moreover, since these are various hues of white, i.e. blue white, yellow white, etc., trace amounts of blue pigment may be added to the cover stock composition to impart a blue white appearance thereto. However, if different hues of the color white are desired, different pigments can be added to the cover composition at the amounts necessary to produce the color desired.
In addition, it is within the purview of this invention to add to the cover compositions of this invention compatible materials which do not affect the basic novel characteristics of the composition of this invention. Among such materials are antioxidants (i.e. Santonox R), antistatic agents, stabilizers and processing aids. The cover compositions of the present invention may also contain softening agents, such as plasticizers, etc. and reinforcing materials such as glass fibers and inorganic fillers, as long as the desired properties produced by the golf ball covers of the invention are not impaired.
Furthermore, optical brighteners, such as those disclosed in U.S. Pat. No. 4,679,795, may also be included in the cover composition of the invention. Examples of suitable optical brighteners which can be used in accordance with this invention are Uvitex OB as sold by the Ciba-Geigy Chemical Company, Ardaley, N.Y. Uvitex OB is thought to be 2,5-Bis(5-tert-butyl-2-benzoxazoly)thiopene. Examples of other optical brighteners suitable for use in accordance with this invention are as follows: Leucopure EGM as sold by Sandoz, East Hanover, N.J. 07936. Leucopure EGM is thought to be 7-(2h-naphthol(1,2-d)-triazol-2yl)-3phenyl-coumarin. Phorwhite K-20G2 is sold by Mobay Chemical Corporation, P.O. Box 385, Union Metro Park, Union, N.J. 07083, and is thought to be a pyrazoline derivative, Eastobrite OB-1 as sold by Eastman Chemical Products, Inc. Kingsport, Tenn., is thought to be 4,4-Bis(benzoxaczoly)stilbene. The above-mentioned Uvitex and Eastobrite OB-1 are preferred optical brighteners for use in accordance with this invention.
Moreover, since many optical brighteners are colored, the percentage of optical brighteners utilized must not be excessive in order to prevent the optical brightener from functioning as a pigment or dye in its own right.
The percentage of optical brighteners which can be used in accordance with this invention is from about 0.01% to about 0.5% as based on the weight of the polymer used as a cover stock. A more preferred range is from about 0.05% to about 0.25% with the most preferred range from about 0.10% to about 0.020% depending on the optical properties of the particular optical brightener used and the polymeric environment in which it is a part.
Generally, the additives are admixed with a ionomer to be used in the cover composition to provide a masterbatch (M.B.) of desired concentration and an amount of the masterbatch sufficient to provide the desired amounts of additive is then admixed with the copolymer blends.
The cover compositions of the present invention may be produced according to conventional melt blending procedures. In this regard, the above indicated high acid ionomeric resins and ionomer resins containing a comonomer of the acrylate ester class are blended along with the masterbatch containing the desired additives in a Banbury type mixer, two-roll mill, or extruded prior to molding. If the xe2x80x9cin-situxe2x80x9d process is utilized, the cations are first blended and are then added to the acid copolymer/acid terpolymer mixture in the Banbury mixer. The blended composition is then formed into slabs or pellets, etc. and maintained in such a state until molding is desired. Alternatively a simple dry blend of the pelletized or granulated resins and color masterbatch may be prepared and fed directly into the injection molding machine where homogenization occurs in the mixing section of the barrel prior to injection into the mold. If necessary, further additives such as an inorganic filler, etc., may be added and uniformly mixed before initiation of the molding process.
Moreover, golf balls of the present invention can be produced by molding processes currently well known in the golf ball art. Specifically, the golf balls can be produced by injection molding or compression molding the novel cover compositions about wound or solid molded cores to produce a golf ball having a diameter of about 1.680 inches or greater and weighing about 1.620 ounces. The standards for both the diameter and weight of the balls are established by the United States Golf Association (U.S.G.A.). Although both solid core and wound cores can be utilized in the present invention, as a result of their lower cost and superior performance, solid molded cores are preferred over wound cores.
Conventional solid cores are typically compression molded from a slug of uncured or lightly cured elastomer composition comprising a high cis content polybutadiene and a metal salt of an xcex1, xcex2, ethylenically unsaturated carboxylic acid such as zinc mono or diacrylate or methacrylate. To achieve higher coefficients of restitution in the core, the manufacturer may include a small amount of a metal oxide such as zinc oxide. In addition, larger amounts of metal oxide than those that are needed to achieve the desired coefficient may be included in order to increase the core weight so that the finished ball more closely approaches the U.S.G.A. upper weight limit of 1.620 ounces. Other materials may be used in the core composition including compatible rubbers or ionomers, and low molecular weight fatty acids such as stearic acid. Free radical initiator catalysts such as peroxides are admixed with the core composition so that on the application of heat and pressure, a complex curing or cross-linking reaction takes place.
The term xe2x80x9csolid coresxe2x80x9d as used herein refers not only to one piece cores but also to those cores having a separate solid layer beneath the cover and above the core as in U.S. Pat. No. 4,431,193, and other multilayer and/or non-wound cores (such as those described in U.S. Pat. No. 4,848,770).
Wound cores are generally produced by winding a very large elastic thread around a solid or liquid filled balloon center. The elastic thread is wound around the center to produce a finished core of about 1.4 to 1.6 inches in diameter, generally. Since the core material is not an integral part of the present invention, a detailed discussion concerning the specific types of core materials which may be utilized with the cover compositions of the invention are not specifically set forth herein. In this regard, the cover compositions of the invention may be used in conjunction with any standard golf ball core.
As indicated, the golf balls of the present invention may be produced by forming covers consisting of the compositions of the invention around cores by conventional molding processes. For example, in compression molding, the cover composition is formed via injection at about 380xc2x0 F. to about 450xc2x0 F. into smooth surfaced hemispherical shells which are then positioned around the core in a dimpled golf ball mold and subjected to compression molding at 200-300xc2x0 F. for 2-10 minutes, followed by cooling at 50-70xc2x0 F. for 2-10 minutes, to fuse the shells together to form an unitary ball. In addition, the golf balls may be produced by injection molding, wherein the cover composition is injected directly around the core placed in the center of a golf ball mold for a period of time at a mold temperature of from 50xc2x0 F. to about 100xc2x0 F. After molding the golf balls produced may undergo various further finishing steps such as buffing, painting, and marking as disclosed in U.S. Pat. No. 4,911,451.
The present invention is further illustrated by the following examples in which the parts of the specific ingredients are by weight (pbw). It is to be understood that the present invention is not limited to the examples, and various changes and modifications may be made in the invention without departing from the spirit and scope thereof.